The purpose of this review is to provide a concise overview of developments over the last 15 years in the field of laboratory tests in human medicine that are based on the detection of alterations in the glycan part of glycoconjugates. We show how glycosylation-based diagnostic testing is widespread in the current clinical practice, in different formats. To provide the necessary focus in this extremely broad field, we have only included assays that are either in actual clinical use or that are under active development towards clinical use, with some bias towards assays that were recently developed. The fields included are: cancer, infectious disease, genetic defects of glycoconjugate biosynthesis and catabolism, auto-immunity, drug abuse and liver disease. To conclude this review, we provide a viewpoint on the future of the glyco-diagnostics field in terms of novel technologies, especially with regard to the discovery and clinical implementation of biomarkers that are based on pathologically altered endogenous glycotopes.